Light which strikes a leaf may be :- Reflected Transmitted – pass straight through Absorbed

1. Light striking a leaf Reflected Absorbed Transmitted • Light which strikes a leaf may be :- • Reflected • Transmitted – pass straight through • Absorbed • White light is a mixture of wavelengths which show up as different colours when light is passed through a prism

2. Components of light emerge to form a pattern of colours called a spectrum Beam of white light. eg. daylight 750 400 600 650 450 350 500 700 550 Wavelength of light (nm ) When white light is passed through leaf pigments certain colours are absorbed and disappear from the light spectrum. This gives rise to the absorption spectrum -see Handout 1

3. Solvent Front Carotene ( Orange ) Xanthophyll ( Yellow ) Chlorophyll a ( Blue-green ) Chlorophyll b ( Dark green ) Spot Line Concentrated Chlorophyll Spot Leaves contain a mixture of pigments :-

4. A detailed absorption spectrum can be produced for each pigment

5. Amount of Photosynthesis (arbitrary units) 440 600 640 480 400 520 680 720 560 Wavelength of illumination (nm ) Chlorophyll a and b absorb in the blue and red end Carotenoids such as xanthophyll and carotene absorb light in other regions e.g. green Accessory pigments such as the carotenoids absorb some light from other regions of the spectrum and pass the energy on to the chlorophyll. A range of pigments are desirable as this increases the total quantity of light absorbed by a plant. Another type of spectrum can be done, where the rate of photosynthesis is measured at different wavelengths. This is called an Action Spectrum

6. Comparison of Absorption and Action Spectrum OHP/Handout X Relative rate of Photosynthesis (arbitrary units) Relative absorption of light (arbitrary units) 440 600 640 480 520 680 720 560 400 Wavelength of light (nm ) • The absorption spectrum shows that light is absorbed in blue and red ends of the spectrum by chlorophyll • The action spectrum shows that light absorbed by chlorophyll is used for photosynthesis • The absorption spectrum shows that light is absorbed in green areas of spectrum by carotenoids ( X ) • The action spectrum shows that the light absorbed by carotenoids in not used directly for photosynthesis

7. Leaf pigments are found in the grana of chloroplasts Lamella – part of inner membrane Stroma Granum – contains chlorophyll Starch Grain Double Membrane

8. Features of a chloroplast Smooth outer membrane Highly folded inner membrane which forms layers Layers contain areas where the membranes are far apart and full of chlorophyll, these are called grana. The fluid filled interior is called stroma.